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The Solo 100 is the design example pursued in the GAD book, which culminated in a playable chassis version of the amp. During several months of playing it that way, I thought about how to finish the amp. This is the result. The circuit board is updated to v4.3 and it include additional panel controls. A new spring reverb card is added to the amp, and a maple wood cabinet finishes the amp with a clean simple design. More details are below.
The Solo 100 is the design example pursued in the GAD book, which culminated in a playable chassis version of the amp. During several months of playing it that way, I thought about how to finish the amp. This is the result. The circuit board is updated to v4.3 and it include additional panel controls. A new spring reverb card is added to the amp, and a maple wood cabinet finishes the amp with a clean simple design. More details are below.
PCB and Circuit updates
PCB and Circuit updates
The v4.3 PCB includes several changes from the book version. Together these changes refine the original design, adding performance improvements and flexibility. The five major changes include:
The v4.3 PCB includes several changes from the book version. Together these changes refine the original design, adding performance improvements and flexibility. The five major changes include:
The color-stage driver JFETs are replaced by LND150 circuits (Q7 and Q8), adding additional headroom and dynamic range.
The color-stage driver JFETs are replaced by LND150 circuits (Q7 and Q8), adding additional headroom and dynamic range.
The driver-stage (Q6) gain is increased for more sustain and higher OD levels.
The driver-stage (Q6) gain is increased for more sustain and higher OD levels.
Three tilt-levels (low, med, high) are now available as switch (S2) options.
Three tilt-levels (low, med, high) are now available as switch (S2) options.
Switch (S3) options now modify the signal levels into the color-stage drivers. Two settings emphasize either the cold or warm-biased OD stages. The third setting drives both OD stages equally.
Switch (S3) options now modify the signal levels into the color-stage drivers. Two settings emphasize either the cold or warm-biased OD stages. The third setting drives both OD stages equally.
Signal (J6) Power (J5) connectors are added to the PCB to support the SoloVerb 3 reverb card.
Signal (J6) Power (J5) connectors are added to the PCB to support the SoloVerb 3 reverb card.
The v4.3 schematics are shown below:
The v4.3 schematics are shown below:
Reverb addition
Reverb addition
After considering and designing several options, I settled on a general-purpose reverb card that is tailored to fit the Solo 100 amp. The card is configured as a “daughter card” to fit on top of a Solo 100 PCB. It fits on standoffs that extend from Solo 100 PCB mounting screws. Of course, it can also be mounted in other amps and chassis.
After considering and designing several options, I settled on a general-purpose reverb card that is tailored to fit the Solo 100 amp. The card is configured as a “daughter card” to fit on top of a Solo 100 PCB. It fits on standoffs that extend from Solo 100 PCB mounting screws. Of course, it can also be mounted in other amps and chassis.
The Solo 100 has an FX jack that passes its signal to the phase inverter (PI). That PI input signal has a useful dynamic range of 0-2.5 V peak. Anything over 2.5 V peak will overdrive and clip the AOT output stage and the PI. Since this dynamic range is well withing the 36 V supply range, the reverb circuit can be simplified by using opamps and a few discrete components. The card drives a standard spring pan and recovers (boosts) the pan signal and mixes it with the original dry signal at unity gain.
The Solo 100 has an FX jack that passes its signal to the phase inverter (PI). That PI input signal has a useful dynamic range of 0-2.5 V peak. Anything over 2.5 V peak will overdrive and clip the AOT output stage and the PI. Since this dynamic range is well withing the 36 V supply range, the reverb circuit can be simplified by using opamps and a few discrete components. The card drives a standard spring pan and recovers (boosts) the pan signal and mixes it with the original dry signal at unity gain.
The SoloVerb3 is designed to be inserted into the signal path between the FX jack and the PI. Think of it as a second FX interface. It could simply be plugged into the FX jack, as in my Teluxe and V-45 designs, but in this case the FX jack remains free for other effects and all the reverb connections are made inside the chassis. The new v4.3 PCB provides circuit board connectors for the reverb card.
The SoloVerb3 is designed to be inserted into the signal path between the FX jack and the PI. Think of it as a second FX interface. It could simply be plugged into the FX jack, as in my Teluxe and V-45 designs, but in this case the FX jack remains free for other effects and all the reverb connections are made inside the chassis. The new v4.3 PCB provides circuit board connectors for the reverb card.
The card is small (2.7” x 2.2”) so it’s not difficult to find mounting space for the card. The card has connectors for power (+36 V and Gnd) and signal input and output. It also has a set of two RCA jacks (red and white) for connecting to a standard 8- or 10-ohm reverb pan. A reverb level control is PCB-mounted to facilitate mounting the card against the front panel. (In other amps, the card could be mounted anywhere, with a shielded cable connecting the level control to the card.)
The card is small (2.7” x 2.2”) so it’s not difficult to find mounting space for the card. The card has connectors for power (+36 V and Gnd) and signal input and output. It also has a set of two RCA jacks (red and white) for connecting to a standard 8- or 10-ohm reverb pan. A reverb level control is PCB-mounted to facilitate mounting the card against the front panel. (In other amps, the card could be mounted anywhere, with a shielded cable connecting the level control to the card.)
The card circuits are fairly simple. The input is AC coupled into a ~5 watt power amp that drives the pan. The pan only needs and receives a fraction of that power and a 2.5 V peak input produces clean (unclipped) signals to the pan. The input signal also connects to the output mixer stage at unity gain, so the card doesn’t affect the dry signal level or fidelity.
The card circuits are fairly simple. The input is AC coupled into a ~5 watt power amp that drives the pan. The pan only needs and receives a fraction of that power and a 2.5 V peak input produces clean (unclipped) signals to the pan. The input signal also connects to the output mixer stage at unity gain, so the card doesn’t affect the dry signal level or fidelity.
The power amp is an equalized voltage source with a series resistance (R10) to raise the drive impedance. Equalization (C1, R2, R3) and the series resistance lead to maximum pan drive power at ~1 KHz. Pan power vs. frequency is sometimes overlooked in reverb driver circuits, but it’s important since it keeps the transducer from saturating or overloading.
The power amp is an equalized voltage source with a series resistance (R10) to raise the drive impedance. Equalization (C1, R2, R3) and the series resistance lead to maximum pan drive power at ~1 KHz. Pan power vs. frequency is sometimes overlooked in reverb driver circuits, but it’s important since it keeps the transducer from saturating or overloading.
The pan output signal is amplified and equalized prior to the reverb level control. Equalization emphasizes the upper-mids and highs that are prevalent in actual room reverberation and are the best sounding components of the pan signal. The mixing stage sums the reverb signal with the dry signal and provides a low-impedance output to drive the Solo PI stage.
The pan output signal is amplified and equalized prior to the reverb level control. Equalization emphasizes the upper-mids and highs that are prevalent in actual room reverberation and are the best sounding components of the pan signal. The mixing stage sums the reverb signal with the dry signal and provides a low-impedance output to drive the Solo PI stage.
The circuit is nothing fancy, but it works really well. Dry signal fidelity is completely preserved. Pan drive power is high and controlled over the guitar frequency range. High pan drive power creates full-sounding reverb with all the rich tone the pan springs can muster.
The circuit is nothing fancy, but it works really well. Dry signal fidelity is completely preserved. Pan drive power is high and controlled over the guitar frequency range. High pan drive power creates full-sounding reverb with all the rich tone the pan springs can muster.
The schematic is below:
The schematic is below:
The PC board is quite small, as shown below with ChapStick for scale.
The PC board is quite small, as shown below with ChapStick for scale.
Below is a picture of the SoloVerb3 PCB mounted in the Solo 100 chassis. The card is supported by standoffs that fit the Solo PCB mounting holes.
Below is a picture of the SoloVerb3 PCB mounted in the Solo 100 chassis. The card is supported by standoffs that fit the Solo PCB mounting holes.
The green terminal block is for the input/output/ground connections via a short 2-conductor shielded cable (white).
The green terminal block is for the input/output/ground connections via a short 2-conductor shielded cable (white).
The blue terminal block is for 36 V power and ground.
The blue terminal block is for 36 V power and ground.
Matching signal and power connections are on the Solo 100 PCB.
Matching signal and power connections are on the Solo 100 PCB.
Reverb is a great addition. The SoloVerb3 daughter card concept worked out well and seems a useful concept to keep in mind for future designs. Most important, the reverb tone quality is exceptional and adds a new dimension to the Solo 100.
Reverb is a great addition. The SoloVerb3 daughter card concept worked out well and seems a useful concept to keep in mind for future designs. Most important, the reverb tone quality is exceptional and adds a new dimension to the Solo 100.
Head cabinet
Head cabinet
The cabinet design is based on the chassis described in the GAD book. That chassis is a U-shaped metal frame that forms the front, bottom, and back panels. The wood cabinet design forms a U-shaped frame that adds a top and two side panels. Additionally, the metal chassis is extended with two perforated sections (front and back) for ventilation.
The cabinet design is based on the chassis described in the GAD book. That chassis is a U-shaped metal frame that forms the front, bottom, and back panels. The wood cabinet design forms a U-shaped frame that adds a top and two side panels. Additionally, the metal chassis is extended with two perforated sections (front and back) for ventilation.
The image below shows the vent sections attached above the front and back panels. Also visible are the angle brackets (.5"x.5") that attach the back panels to the birdseye maple sides. Similar brackets (not visible) attach the front panel to the sides. The maple sides are sanded smooth and finished with clear poly. The front panel graphics are printed on a thin (.030) aluminum plate. Close inspection shows internal heat sinks on the back panel to promote cooling.
The image below shows the vent sections attached above the front and back panels. Also visible are the angle brackets (.5"x.5") that attach the back panels to the birdseye maple sides. Similar brackets (not visible) attach the front panel to the sides. The maple sides are sanded smooth and finished with clear poly. The front panel graphics are printed on a thin (.030) aluminum plate. Close inspection shows internal heat sinks on the back panel to promote cooling.
The top panel is white maple and sits on the vents. A leather strap is attached to the top-side of the panel.
The top panel is white maple and sits on the vents. A leather strap is attached to the top-side of the panel.
The inner surface has two glued chocks flush to the side panels. A spring reverb pan is mounted between the two chocks as shown in the image below.
The inner surface has two glued chocks flush to the side panels. A spring reverb pan is mounted between the two chocks as shown in the image below.
Screws pass through the side panels and into the chocks to attach the top panel to the sides.
Screws pass through the side panels and into the chocks to attach the top panel to the sides.
Power Supply
Power Supply
The GAD book design used two DC converters to create the 360 V power source for the amp. In this version, a simpler DC converter that operates directly from 36 V is used. The converter is described here and the image below shows it mounted in the Solo chassis. Use of this converter reduces complexity and simplifies chassis wiring.
The GAD book design used two DC converters to create the 360 V power source for the amp. In this version, a simpler DC converter that operates directly from 36 V is used. The converter is described here and the image below shows it mounted in the Solo chassis. Use of this converter reduces complexity and simplifies chassis wiring.
The updated Solo amp is a "personal best". It sounds and looks great and it's a pleasure to play.
The updated Solo amp is a "personal best". It sounds and looks great and it's a pleasure to play.
The simplicity of design and execution fulfill the goals of the GAD project. Mechanical construction is simple. Sheet metal (0.063) is purchased precut so only drilling and bending is required. The three wood panels are simple rectangles so they're easy to cut. Everything fits together with four angle brackets. The complete 100-watt head weighs only 8.4 pounds.
The simplicity of design and execution fulfill the goals of the GAD project. Mechanical construction is simple. Sheet metal (0.063) is purchased precut so only drilling and bending is required. The three wood panels are simple rectangles so they're easy to cut. Everything fits together with four angle brackets. The complete 100-watt head weighs only 8.4 pounds.
The amp, reverb, and DC converter PCBs are available, as are CAD drawings and BOM files. Contact me for details.
The amp, reverb, and DC converter PCBs are available, as are CAD drawings and BOM files. Contact me for details.
David Anderson constructed a new version of this amp with a new tremolo feature. See details here.
David Anderson constructed a new version of this amp with a new tremolo feature. See details here.
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